A photonic crystal comprises an artificially engineered periodic dielectric array having at least one photonic bandgap, i.e., a range of frequencies in which ordinary electromagnetic wave propagation is strictly forbidden. The presence of these photonic bandgaps can be used to confine and guide electromagnetic waves for any of a variety of useful purposes. Guidance and confinement are achieved by the judicious introduction of defect regions, i.e., missing or differently-shaped portions of the periodic array, within which the electromagnetic waves are permitted to exist and wherealong the electromagnetic waves can be confined and guided. Photonic crystals have a growing variety of promising uses as incorporated, for example, into optical switches, optical transistors, beam splitters, optically resonant cavities, and small-footprint optical circuits. Photonic crystals can exhibit special properties such as a so-called superprism effect in which, for certain wavelengths, very small changes in the angle of incidence can cause very large changes in the angle of refraction. Proposals have even been made for negatively refracting photonic crystals, bringing about the possibility of so-called flat lenses or superlenses unfettered by diffraction limitations or alignment issues.
Proposals have been made for fabricating photonic crystals in various ways, including lithographically etching channels in a slab of dielectric material, and including lithographically forming posts and depositing slab material around the posts. However, especially as patterns continue to shrink, issues continue to arise in relation to one or more of the following: forming deep enough channels with sufficiently vertical walls; limitations in the choice of slab materials that can be anisotropically etched to form channels; physical limitations of such slab materials that, in turn, can impose limitations on modulation schemes that might be realized; limited tunability of critical parameters during and after the fabrication process; and, more generally, material cost, device yields, fabrication cost, and design flexibility. Other issues remain as would be apparent to one skilled in the art upon reading the present disclosure.